The present invention is directed toward an improved master cylinder lever for a hydraulic disc brake, and more particularly to a dead-band adjustment mechanism.
Virtually all known bicycle hydraulic disc brake master cylinders operate in the same basic way. A piston is movable within a cylinder from a start position near a first end of the cylinder to a pressurized position near a second end of the cylinder. Between the first and second ends of the cylinder is a timing port in fluid communication between the cylinder interior and a hydraulic fluid reservoir. As the piston moves from the start position toward the timing port, hydraulic fluid flows from the timing port to the reservoir. Once a seal associated with the piston moves between the timing port and the second end of the cylinder, fluid within the second end of the cylinder and hydraulic lines in fluid communication with a caliper become pressurized and the caliper is actuated. The travel between the start position of the piston and the timing port is known as the xe2x80x9cdead-bandxe2x80x9d.
Different structures are known for varying the amount of dead-band in accordance with user preferences. For example, it is known to physically alter the start position of the piston within the cylinder to vary the dead-band. However, such structures also result in movement of the start position of a lever handle operatively associated with the piston. This results in variation of the xe2x80x9creachxe2x80x9d between the handle and the handlebar. This can be bothersome to riders and require the riders to readjust the reach after changing the dead-band.
The present invention is directed to overcoming one or more of the problems discussed above.
The first aspect of the present invention is a master cylinder for a hydraulic disc brake having a housing defining a cylinder, with the cylinder having a first and a second end. A port provides fluid communication between the cylinder and a hydraulic fluid reservoir. The port has a port opening located between the first and second ends of the cylinder. A piston is received in the cylinder and has a radial seal. The piston is movable between a select starting position with the seal between the first end and the port opening with the seal a select distance from the port opening and a pressurized position with the seal between the port opening and the second end. The radial seal prevents fluid flow between the cylinder and the reservoir when positioned between the port opening and the second end to pressurize the second end. A dead-band adjustment structure is operatively associated with the piston for moving the select starting position to adjust the select distance between the port opening and the seal. A lever is pivotably attached to the housing and is operatively associated with the piston to move the piston between the select starting position and the pressurized position as the lever is pivoted between a rest position and a fully-actuated position. A compensating structure is operatively associated with the dead-band adjustment structure and the lever to maintain the lever in a select rest position as the dead-band adjustment structure is actuated to move the select starting position.
The master cylinder may include a push rod having a second end operatively associated with the piston and a first end operatively associated with the lever to translate pivotal movement of the lever to axial movement of the piston within the cylinder. In this embodiment, the dead-band adjustment structure preferably includes a threaded member threadably engaging the housing axially of the first end of the cylinder. The threaded member has an axial bore receiving the push rod and the push rod and the threaded member are configured so that axial rotation of the threaded member in a first direction moves the push rod toward the second end of the cylinder and axial rotation in a second direction moves the push rod away from the second end of the cylinder.
The master cylinder may further include a reach adjustment structure in operative association with the lever for varying the rest position of the lever to adjust the reach of the lever independent of movement of the select starting position of the piston. The reach adjustment structure preferably includes a push rod and a cross dowel. The push rod has a second end operatively associated with the piston and an axially threaded first end. The cross dowel is received in the lever for pivoting about a cross dowel axis transverse the axis of the cylinder. The cross dowel has an internally threaded bore transverse the cross dowel axis and the internally threaded bore threadably receives the axially threaded first end of the push rod. Axial rotation of the push rod moves the cross dowel axially of the push rod to pivot the lever about its pivot and to thereby move the rest position of the lever to adjust the lever reach. Preferably, an axis of the internally threaded bore of the cross dowel does not intersect the cross dowel axis.
The master cylinder may also include a structure for operatively disassociating the second end of the push rod from the piston as the lever is pivoted away from the select rest position in a direction away from the fully-actuated position.
A second aspect of the present invention is a master cylinder for a bicycle hydraulic disc brake, the master cylinder including a housing defining a cylinder having a first end and a second end along a cylinder axis. A port provides fluid communication between a hydraulic fluid reservoir and the cylinder. The port has a port opening located between the first and second ends of the cylinder. A piston having a radial seal is axially received in the cylinder and is movable between a select starting position with the seal between the port opening and the first end of the cylinder and a pressurized position with the seal between the port opening and the second end of the cylinder. The seal prevents fluid flow between the reservoir and the second end of the cylinder when positioned between the port opening and the second end of the cylinder to pressurize the second end of the cylinder. A lever is pivotably connected to the housing to pivot about an axis transverse the cylinder axis between a rest position and a fully-actuated position. A push rod has a threaded portion near a first end threadably connected to the lever and a second end operatively associated with the piston so that as the lever is pivoted between the rest position and the fully-actuated position the piston is moved between the starting position and the pressurized position. An externally threaded insert is threadably received in the housing along the cylinder axis. The externally threaded insert is operatively associated with the push rod to move the second end of the push rod along the cylinder axis toward the second end of the cylinder as the externally threaded insert is rotated in a first direction within the housing and to move the second end of the push rod away from the second end of the cylinder as the externally threaded insert is rotated in a second direction within the housing, whereby the select starting position of the piston may be selected by a user. The threaded connection between the threaded portion of the push rod and the lever is configured to maintain the lever in a select rest position relative to the housing as the externally threaded insert and thereby the push rod are rotated in either of the first and second directions to vary the select start position of the piston.
The externally threaded insert may include a first externally threaded axial portion threadably engaged with the housing and a second axial portion having radially extending gear teeth inclined axially and configured to engage with a worm. The worn preferably has a knob and the worm is attached to the housing for rotation by the knob about an axis transverse the cylinder axis. In this manner, as the worm is rotated by the knob the externally threaded insert is rotated relative to the housing to thereby move the starting position of the piston. The externally threaded insert preferably has an axial bore receiving the push rod. The axial bore preferably has a conical sidewall configured to allow pivoting of the push rod relative to the threaded insert as the lever is actuated.
The threaded connection between the threaded portion of the push rod and the lever preferably consists of a cross dowel pivotably received in the lever for pivoting about a dowel axis parallel to the lever pivot axis. The cross dowel has an internally threaded bore transverse the dowel axis which threadably receives the threaded portion of the push rod. The internally threaded bore preferably has an axis that does not intersect with the dowel axis.
The master cylinder lever of the present invention provides for dead-band adjustment by a user while compensating for otherwise resulting movement of the lever handle to enable adjustment of the dead-band without movement of the start position of the lever handle. In this way, a user selected lever handle reach is unaffected by variation of the piston start position. The master cylinder of the present invention also provides for adjustment of the reach without movement of the start position of the piston to allow a user to vary lever reach without affecting a pre-selected dead-band. The master cylinder lever also includes an off-axis cross dowel structure which prevents undesired variation of the user selected reach due to vibration or other operative forces on the lever during use. These and other advantages are provided without significantly increasing the cost or complexity of assembly of the master cylinder.